[Paper Review] Performance enhancement of TiO2-based dye-sensitized solar cells by carbon nanospheres in photoanode

Elham Bayatloo, Esmaiel Saievar-Iranizad|arXiv (Cornell University)|Nov 2, 2013

Chemical and Physical Properties of Materials1 references4 citations

TL;DR

This study enhances TiO2-based dye-sensitized solar cells (DSSCs) by incorporating carbon nanospheres (100–600 nm) into the TiO2 photoanode paste, which are later removed during sintering to create controlled porosity. The resulting cavities improve light scattering and dye loading, boosting efficiency by 33% (from 5.72% to 7.59%) and short-circuit current density by 40% (12.59 to 17.73 mA/cm²) at 3 wt.% carbon nanospheres.

ABSTRACT

The conversion efficiency of dye-sensitized solar cells (DSSCs) is optimized by modifying the optical design and improving absorbance within the cell. These objectives are obtained by creating different sized cavities in TiO2 photoanode. For this purpose, carbon nanospheres with diameters 100-600 nm are synthesized by hydrothermal method. A paste of TiO2 is mixed with various amounts of carbon nanospheres. During TiO2 photoanode sintering processes at 500C temperature, the carbon nanospheres are removed. This leads to random creation of cavities in the DSSCs photoanode. These cavities enhance light scattering and porosity which improve light absorbance by dye N719 and provide a larger surface area for dye loading. These consequences enhance performance of DSSCs. By mixing 3% Wt. carbon nanospheres in the TiO2 pastes, we were able to increase the short circuit current density and efficiency by 40% (from 12.59 to 17.73 mA/cm2) and 33% (from 5.72% to 7.59%), respectively.

Motivation & Objective

• To improve the power conversion efficiency of TiO2-based dye-sensitized solar cells (DSSCs) through enhanced light harvesting and dye loading.
• To address limitations in light absorption and electron recombination by engineering photoanode microstructure.
• To investigate the role of controlled porosity via sacrificial carbon nanospheres in optimizing optical and electronic properties.
• To identify the optimal carbon nanosphere concentration that maximizes efficiency without increasing recombination.

Proposed method

• Synthesized carbon nanospheres (100–600 nm) via hydrothermal method using glucose as precursor.
• Prepared TiO2 pastes with 0%, 1%, 2%, 3%, and 4% weight fractions of carbon nanospheres in ethanol.
• Fabricated FTO-embedded TiO2 photoanodes using doctor-blade technique and sintered at 500°C, where carbon nanospheres were combusted to form pores.
• Deposited N719 dye onto the photoanodes via immersion in 0.4 mM dye solution for 20–24 hours.
• Performed incident photon-to-current efficiency (IPCE), electrochemical impedance spectroscopy (EIS), and dye desorption measurements to evaluate performance.
• Used EIS data to extract chemical capacitance (Cμ) and recombination resistance (Rrec) to analyze charge transfer dynamics.

Experimental results

Research questions

• RQ1 How does the incorporation of carbon nanospheres affect light scattering and optical path length in the TiO2 photoanode?
• RQ2 What is the optimal weight percentage of carbon nanospheres that maximizes dye loading and minimizes recombination?
• RQ3 How does porosity from carbon nanosphere removal influence electron recombination and open-circuit voltage (VOC)?
• RQ4 To what extent does the presence of large and small cavities enhance incident photon-to-current conversion efficiency (IPCE) and short-circuit current density (JSC)?
• RQ5 Does the engineered porosity alter the TiO2 density of states or conduction band edge position?

Key findings

• At 3 wt.% carbon nanospheres, the short-circuit current density increased by 40%, from 12.59 mA/cm² to 17.73 mA/cm².
• The power conversion efficiency improved by 33%, reaching 7.59% compared to 5.72% for the control (0 wt.%).
• The IPCE spectrum for the 3 wt.% sample showed a broadened response from 400–600 nm and a peak increase from 30% to 60%.
• EIS analysis revealed that the T3 (3 wt.%) sample had the highest recombination resistance (Rrec), correlating with its highest open-circuit voltage.
• Dye desorption measurements confirmed increased dye loading in porous photoanodes, peaking at 3 wt.%.
• Chemical capacitance (Cμ) remained nearly constant across all samples, indicating no shift in the TiO2 conduction band edge due to porosity.